Jacking devices are used in a variety of applications for raising and lowering objects. One such application is to raise and lower one end of an automobile or other vehicle so as to be able to change a flat tire or to facilitate access to components on the underside of the vehicle. Another application is to support the front end of a boat trailer or the like while the trailer is disengaged from a tow vehicle such as a truck.
Jacking devices are typically comprised of an elongated toothed shaft, which mates with a user-operable jacking gear. The gear is operated by means of a rotatable handle or the like, which in turn rotates a worm gear mechanism, thereby causing the toothed shaft to migrate up or down along the toothed shaft to raise or lower the object supported by the jack, as the case may be. When a jack is used to support a boat trailer, the worm gear mechanism is typically fixed with respect to the trailer so that the toothed shaft moves up and down with respect to the trailer. Attached to the lower end of the shaft is a wheel for contacting the ground to support the jack. When it is desired to raise the level of the trailer, the wheel is positioned in contact with the ground and the shaft is lowered by the action of the worm gear until the trailer reaches the desired height. When the trailer is attached to a bumper hitch or the like on a tow vehicle, such as a truck, the shaft and wheel are raised so that the wheel does not contact the ground during transportation.